Just about any camping trip around Seattle will have plenty to explore–woods, lakes, your spirit, etc..
Map points are ordered north to southwest.
You’ll discover a lot of them clustered round the Admiralty Inlet, forts from a former military attempt to thwart intrusion by sea, for example all three temples of the”Triangle of Fire” (What was strategic siting is now prime waterfront locations.) If you prefer your outings to not come with a side of warfare, however, there are still a few alternatives.
Just looking to get a trekking trip?
National, state, and local parks across the area have other relics hanging round, cottages, and loads of military bases, and a number of them even permit camping. No, you probably can’t camp indoors them, but creating a base of operations permits that much more time to research. They’re of various levels of activation too–from museums to art spaces to simply bunkers that are abandoned –to match all tastes.
Some not, some semi-abandoned